mass of NAPol particles is slightly higher as that of A8-35 ones (~50 kDa, as determined by AUC and
SANS, vs. ~40 kDa). As for A8-35, each particle comprises, on average, ~75 alkyl chains (undecyl
ones in the case of NAPols rather than octyl ones in the case of A8-35). Upon AUC, NAPol particles
appear perfectly monodisperse (Fig. 4.28). Both SANS and AUC data are consistent with their being
globular and compact.
It is worth noting that, upon SEC, the particles formed by homotelomeric NAPols elute as a very
sharp peak, much narrower than that formed by A8-35 particles, suggesting a greater size homogeneity
(Fig. 4.28A). This is confirmed by the narrowness of the c(s) distribution in SV-AUC experiments
(Fig. 4.28C). As noted above (§ 4.3.1.2.2), SEC analysis of fractions from a preparative SEC
fractionation of A8-35 suggests that the variability of R S among particles may be due to individual
molecules differing with respect to the extent or distribution of hydrophobic grafting. It is easy to
imagine, for instance, that a large molecule that presents either a surfeit or a deficit of octyl chains will
recruit respectively less or more smaller molecules in order for a core comprising 75–80 alkyl chains to
form. At variance with A8-35, the molecules present in a batch of homotelomeric NAPol differ only in
their length, not in the density nor distribution of alkyl chains. This could possibly lead to a narrower
distribution of particle sizes. Consistent with this hypothesis, particles formed by heterotelomeric
glucosylated NAPols, which are chemically heterogeneous, elute slightly later than A8-35 particles,
as homotelomeric NAPol particles do, but they do not feature a narrower distribution (Sharma
et al. 2008).
No detailed report appears to have been published on NVoy particles. According to unpublished
data cited in the Supplementary Information to Klammt et al. (2011), their mass is ~112 kDa,
corresponding to ~22 molecules.
We lack data to gather to which extent the other kinds of information that have been collected on
A8-35 particles can be extended to other, less thoroughly studied APols. Certain tendencies can be
surmised with some degree of confidence. For instance, it has been a constant observation, with a large
spectrum of preparations of PAA-derived polymers, that samples that do not form by themselves small
monodisperse particles do not yield small monodisperse MP/APol complexes (see Gohon et al. 2008).
The behavior of the polymer alone, therefore, provides a first indication about its probable usefulness
in biochemistry and biophysics. Symmetrically, the observation of small MP/polymer complexes can
be taken as an indication that the polymer is likely to form by itself small particles. Some physicalchemical trends can probably be surmised. For instance, because particle assembly, as does
micellization, forces polar moieties to come in close vicinity one to another, it is reasonable to expect
that increasing the charge density along a given type of chain will raise the CAC (e.g. A8-75 or SAPols
as compared to A8-35), whereas diminishing it or raising the ionic strength will have the reverse effect.
There is a dearth of studies about the composition and organization of APol particles. However, it is
striking that particles of A8-35 and glucose-based NAPols, whose chemical structures and physical
properties are quite different, both comprise some 75–80 alkyl chains (Gohon et al. 2006; Sharma et al.
2012). This number is typical of detergent micelles (Chap. 2) and has also been encountered in studies
of microdomain formation in other amphipathic polymers (Petit-Agnely and Iliopoulos 1999). This
observation can perhaps provide a guideline when designing new APols or trying to guess at the selforganization properties of existing but poorly characterized ones. The sensitivity of APols to pH or
multivalent cations, when it has not been experimentally established, can in general be surmised from
the chemical structure (Table 4.4). Other features, such as solubility, viscosity, or the rate of exchange
of molecules between particles, appear more difficult to anticipate.
4.3 Self-Association Behavior of Amphipols in Aqueous Solutions
197
SANS, vs. ~40 kDa). As for A8-35, each particle comprises, on average, ~75 alkyl chains (undecyl
ones in the case of NAPols rather than octyl ones in the case of A8-35). Upon AUC, NAPol particles
appear perfectly monodisperse (Fig. 4.28). Both SANS and AUC data are consistent with their being
globular and compact.
It is worth noting that, upon SEC, the particles formed by homotelomeric NAPols elute as a very
sharp peak, much narrower than that formed by A8-35 particles, suggesting a greater size homogeneity
(Fig. 4.28A). This is confirmed by the narrowness of the c(s) distribution in SV-AUC experiments
(Fig. 4.28C). As noted above (§ 4.3.1.2.2), SEC analysis of fractions from a preparative SEC
fractionation of A8-35 suggests that the variability of R S among particles may be due to individual
molecules differing with respect to the extent or distribution of hydrophobic grafting. It is easy to
imagine, for instance, that a large molecule that presents either a surfeit or a deficit of octyl chains will
recruit respectively less or more smaller molecules in order for a core comprising 75–80 alkyl chains to
form. At variance with A8-35, the molecules present in a batch of homotelomeric NAPol differ only in
their length, not in the density nor distribution of alkyl chains. This could possibly lead to a narrower
distribution of particle sizes. Consistent with this hypothesis, particles formed by heterotelomeric
glucosylated NAPols, which are chemically heterogeneous, elute slightly later than A8-35 particles,
as homotelomeric NAPol particles do, but they do not feature a narrower distribution (Sharma
et al. 2008).
No detailed report appears to have been published on NVoy particles. According to unpublished
data cited in the Supplementary Information to Klammt et al. (2011), their mass is ~112 kDa,
corresponding to ~22 molecules.
We lack data to gather to which extent the other kinds of information that have been collected on
A8-35 particles can be extended to other, less thoroughly studied APols. Certain tendencies can be
surmised with some degree of confidence. For instance, it has been a constant observation, with a large
spectrum of preparations of PAA-derived polymers, that samples that do not form by themselves small
monodisperse particles do not yield small monodisperse MP/APol complexes (see Gohon et al. 2008).
The behavior of the polymer alone, therefore, provides a first indication about its probable usefulness
in biochemistry and biophysics. Symmetrically, the observation of small MP/polymer complexes can
be taken as an indication that the polymer is likely to form by itself small particles. Some physicalchemical trends can probably be surmised. For instance, because particle assembly, as does
micellization, forces polar moieties to come in close vicinity one to another, it is reasonable to expect
that increasing the charge density along a given type of chain will raise the CAC (e.g. A8-75 or SAPols
as compared to A8-35), whereas diminishing it or raising the ionic strength will have the reverse effect.
There is a dearth of studies about the composition and organization of APol particles. However, it is
striking that particles of A8-35 and glucose-based NAPols, whose chemical structures and physical
properties are quite different, both comprise some 75–80 alkyl chains (Gohon et al. 2006; Sharma et al.
2012). This number is typical of detergent micelles (Chap. 2) and has also been encountered in studies
of microdomain formation in other amphipathic polymers (Petit-Agnely and Iliopoulos 1999). This
observation can perhaps provide a guideline when designing new APols or trying to guess at the selforganization properties of existing but poorly characterized ones. The sensitivity of APols to pH or
multivalent cations, when it has not been experimentally established, can in general be surmised from
the chemical structure (Table 4.4). Other features, such as solubility, viscosity, or the rate of exchange
of molecules between particles, appear more difficult to anticipate.
4.3 Self-Association Behavior of Amphipols in Aqueous Solutions
197